etching to reveal faults in knife blades

[Joe Calton]

https://youtu.be/wkJ2p77cdzg

https://youtu.be/OVB_bPMM0RA

https://youtu.be/QGOWIdFUbYU

did a couple of videos today and yesterday about etching blades to show faults. had a pretty tough time both burning an edge on the grinder on purpose, and showing the damage in the etch, but I think there are a couple shots in there that show it pretty good. it seems like it is easier to see the faults while the blade is still wet from the etchant, both with ferric and vinegar. once the blade dries out, its much tougher to see them.    

[Ed Fowler]

Way to go Joe, that is just what I am writing my article on, your blades will go well with the article.

I believe that the reason you cannot see anything in the steel when you heat with a torch to the sizzle point  is because you are not above the tempering temperature. Still if you can get it to where we can see it we will know something happened.

So many experiments await us, the more makers who have the curiosity and drive to experiment the more we will all learn.

[Joe Calton]

thanks ed.

the knives are in a box and will be headed your way tomorrow so you can take some pictures if you want. I ended up forgetting about one of them in the vinegar tank, and left it there until sometime the next day. it is pretty interesting in that you can really tell the harder parts, and the parts that were either left soft, or were damaged either by the torch or grinder. the hard portions are quite a bit higher than the softer parts :} and the edge where it was overheated has been eaten back into the blade.

another interesting thing is that on the back side of the large parer, there were some deep scratches left in the finish when I went to etch it. Id guess 60 grit. the scratch looks like it wasn't etched at the same rate as the area around it, and they are standing up from the surface. almost as if the grit that caused it, moved the metal around the piece of grit as it cut, work hardening it. as soon as you run your finger over it, it will be pretty obvious.

I was hoping that the part that I just heated to a sizzle would show something, but looking back on it now, the parts that were overheated with a torch or the belt were pretty faint in the camera. and that part of the test was an attempt to get an etch of something like what happens when powergrinding an edge. but it may be that that sort of damage is fairly shallow, and that the etchant may cut the damaged steel away as fast as it reveals it. ill probably try that part of the experiment again sooner or later. maybe with a weaker etchant and higher polish.

[TomWhite]

Thanks Joe. Enjoyed watching, spent an hour or so, so much information.
Though I don't make so many knives it makes me consider how I sharpen
My tools. Often I apply pressure and get the blue edge we see. I now know that
I have changed the heat treat I bought the tool for. Perhaps this is why they
Don't hold an edge like new.
You are giving information that is quite valuable, may save some of my every
Day tools from my rush to sharpen,
Knowledge had many applications and you sure show lots of them.
Thanks again!

[Joe Calton]

thanks Tom! I'm very glad that you enjoyed the videos!

I know everyone sharpens differently, but when I am sharpening with power equipment, I just use it to shape an edge and get it close. with as little pressure and heat as I can get away with, and with coarser belts as they cut faster and cooler. and then do the final sharpening by hand.

and there is always more to learn about sharpening.... just the other day, I learned how, and sharpened my first couple of saws! I believe they are my grandfathers bone saws. the blades were riveted in pretty hard, and so I took about an hour and a half to build a jig to hold the blades still, and then the first saw took me about 10 minutes to sharpen, and the second took about 5 minutes. in todays age of power saws, and disposable blades, it had never occured to me to sharpen a saw. and now that I have the basics down, it is very cool to know how!

[Daniel Rohde (D-Vision)]

Great videos Joe! While I was already aware of most of what you said, I always learn somthing from your videos. Thanks for making them!

[TomWhite]

It is a shame that saw sharping is a lost art. I have a few very old hand saws and they are still sharp.
I would not have a clue as to how bring them back if they get dull.
The idea of using rough grit up front to remove metal makes sense due to reducing heat.
I had never really thought about it, thanks for bringing it to my attention.
 

[Ed Fowler]

Well you see son, in the old days that is the only way we could make them cut more!